1. Field of the Invention
The present invention relates to a method of cutting or perforating a plurality of plate-like materials such as glass, ceramics or another fragile materials to have exactly the same circular shape or an opening having exactly the same dimension.
2. Discussion of Background
Generally, a disk-like glass plate used for an optical disk, a magnetic disk, an optical-magnetoelectric disk or the like has been processed by annularly arranged grindstones. Namely, when a disk-like glass plate is to be obtained, an individual rectangular glass plate was fixed onto a processing table by means of vacuum suction; the annularly arranged grindstones are rotated to thereby cut off a disk-like glass plate from the rectangular glass plate. Namely, the disk-like glass plate was obtained by processing the outer periphery of the rectangular glass plate into a circular shape and/or perforating the inner portion of the disk-like glass plate simultaneously or separately. Recently, the optical disk, the magnetic disk or the like has been miniaturized, and the outer diameter and the wall thickness of the optical disk, the magnetic disk or the like has become thinner.
However, when the outer diameter of the optical disk or the magnetic disk is made smaller to be, for instance, less than 2.5 inches and the thickness of the same is less than 0.05 inches, it is difficult to fix by vacuum suction a rectangular glass plate on a processing table, and accordingly, it is difficult to process the glass plate to be circular or to perforate it. Further, another problem is that since the rectangular glass plate has to be processed one by one to obtain the disk-like glass plate, productivity can not be improved to thereby invite a manufacturing cost increase.
Further, as shown in FIG. 10, when disk-like glass plates 2 are processed individually to have a circular shape or perforation, there easily causes tipping (i.e. breakage of an edge portion) at an inner edge portion 2A or an outer edge portion of the disk-like glass, thereby resulting poor yield.